1. Field of the Invention
This invention relates to constant velocity ratio universal joints of the cross groove type, comprising inner and outer joint members having circumferentially disposed axially extending facing pairs of grooves which receive balls for torque transmission between the joint members, the grooves of each pair being oppositely inclined to the rotational axes of their joint members so that they cross one another as viewed in a direction transverse to such axes, the joint further comprising a cage of annular form disposed between the joint members and having apertures wherein the balls are received to constrain the balls such that their centres occupy a common plane. When the joint is articulated, the configuration of the grooves causes such common plane to bisect the angle between the rotational axes of the joint members, to give the joint the required constant velocity ratio characteristics. The joint is able to accommodate relative axial movement (so called "plunge") between the joint members, the balls moving along the grooves in the joint members during such relative axial movement. Such joints will herein be referred to for convenience simply as cross groove joints.
2. Prior Art
Cross groove joints are sold by the assignee of the present application under the designation VL joints, such joints being useful in universally jointed motor vehicle drive shafts where one of the joints must be capable of accommodating plunge in order to permit installation of a shaft and to allow for geometrical changes with suspension movement in use.
In one known type of cross groove joint (designated as VL-91) the cage for constraining the balls, which is generally in the form of an annular shell with part-spherical internal and external surfaces, has an opening extending through it which is larger than the overall outside diameter of the joint inner member. It is therefore possible to assemble the joint, and in particular to assemble the cage to the inner joint member, simply by feeding the inner joint member axially into the cage. However, when the joint is assembled, the cage cannot engage with the inner joint member to limit the range of plunging movement permitted by the joint. It will be appreciated that, when the joint plunges, the cage moves axially relative to the inner joint member by a distance equal to half the distance by which the inner joint member moves relative to the outer joint member, and if the cage were arranged to engage the inner joint member to prevent relative movement therebetween it would consequently limit movement between the inner and outer joint members.
Therefore, with such a known type of joint, some means has to be provided elsewhere to limit plunge in the joint. For example, if a drive shaft incorporates two plunging joints, the other joint must incorporate some plunge-limiting stops. A further disadvantage of such a joint is that the angle to which the joint can articulate is relatively limited, and the torque transmitting capacity decreases considerably at larger angles of articulation.
In a further known type of cross groove joint (designated VL-107) the cage has at each end an aperture which is smaller than the overall outside diameter of the joint inner member. This requires assembly of the joint by articulation of the cage relative to the inner joint member through an angle greater than that which will occur in service. This also requires some changes in the cross-sectional shape of the ball-receiving grooves in the inner joint member. When a joint of this type is assembled, the cage will co-operate with the inner joint member to limit relative axial movement between these parts, and hence will limit the overall plunging movement which the joint can provide. This is advantageous in operation, but the limit on plunging movement may render installation of a drive shaft equipped with such a joint more difficult. It will be appreciated that to install a drive shaft may require the shaft to be shortened very considerably, necessitating maximum plunge capability in one or both of the joints thereof.